The long term goal of this research is to delineate the mechanism of action of the fibrinolytic system (plasminogen-plasmin) at the molecular level by identifying those features which determine its specific physiological role. Plasminogen is able to bind to fibrin and be incorporated into a clot. This allows subsequent activation to plasmin and lysis to proceed in an inhibitor free environment. This binding to fibrin results from specific binding sites in plasminogen and plasmin which also bind lysine peptides or lysine analogs. These lysine binding sites are also involved in the action of plasmin on a fibrin clot and the inhibition of plasmin by its main physiological inhibitor, Alpha 2-plasmin inhibitor. Among the specific aims of this proposal are to continue our determination of the function of these sites by specific photoaffinity labeling of lysine binding sites in plasminogen-plasmin. Three dimensional information about the structure of plasmin will be obtained by measuring the distance between individual lysine binding sites and the catalytic site using a combination of photoaffinity labeling and fluorescence energy transfer techniques. We will also design and synethesize bifunctional substrates and inhibitors which will mimic the interactions of fibrin and Alpha 2-plasmin inhibitor with plasmin by binding both at the catalytic site and at the lysine binding site which regulates clot lysis. The information from these studies will have potential usefulness in conjunction with current antifibrinolytic and fibrinolytic therapy. The compounds synthesized as part of this research may provide alternate agents for antifibrinolytic therapy. The substrates and inhibitors will also be of value in clarifying the proposed role of the fibrinolytic system in a variety of normal and abnormal physiological processes.